Described is a continuous process comprising a single chemical step for preparing 3-methyl-tetrahydrofuran from alpha-methylene-gamma-butyrolactone.
Substituted tetrahydrofuran, like 3-methyl-tetrahydrofuran of the present invention, is in general useful in those areas in which tetrahydrofuran is used. Examples include polymerization to obtain fibers and uses as a solvent.
Poly (tetra methylene ether glycol) is polymerized to produce tetrahydrofuran. This polymer is used as chain segments in polyurethanes and polyesters. Polyurethanes based on poly (tetra methylene ether glycol) soft-segment have improved hydrolytic stability, abrasion resistance and elastomeric properties. Other benefits include strength, toughness, durability, low compression set property, and high water vapor permeability. The largest end-use area of these polyurethanes is as spandex fibers for apparel. Products containing poly (tetra methylene ether glycol) are also used in wheels, high-speed rolls, automotive parts, bushings, specialty hose, cable sheathing and coating, pipeline liners, and roof and floor coatings. 3-methyl-tetrahydrofuran monomer can be utilized as a comonomer for modifying poly(tetra methylene ether glycol) to yield better elastomeric properties.
In use of tetrahydrofuran as a solvent where lower volatility is desired, 3-methyl-tetrahydrofuran is advantageous because tetrahydrofuran boils at 66xc2x0 C. whereas 3-methyl-tetrahydrofuran boils at 86xc2x0 C.
Processes for producing 3-methyl-tetrahydrofuran, by hydrogenation of an itaconic acid ester or a 3-formyl-2-methylpropionic acid ester, and by hydrogenation of a methyl-succinic ester are described in Japanese Patent Applications 219981/1994 and 217768/1996, respectively. Along with the objective 3-methyl-tetrahydrofuran, these reactions produce an alcohol, which has to be separated in a further step. The 3-methyl-tetrahydrofuran forms an azeotropic mixture with most of the lower alcohols, for example, with methanol having an azeotropic point at 64.5xc2x0 C., and an azeotropic composition consisting of 25% by weight of 3-methyl-tetrahydrofuran and 75% by weight of methanol. The existence of this azeotrope necessitates a costly, energy intensive separation step to yield pure 3-methyl-tetrahydrofuran. In particular, the 3-methyl-tetrahydrofuran which is employed for modifying poly(tetramethylene glycol) can tolerate an alcohol impurity of less than 0.2%.
Similarly, U.S. Pat. No. 5,990,324 describes a process for producing 3-methyltetrahydrofuran by hydrogenation of beta-formylisobutyric acid ester with the general formula ROOCxe2x80x94CH(CH3)xe2x80x94CH2xe2x80x94CHO wherein, R is an alkyl group having 1 to 3 carbon atoms and the formyl group may be present as an acetal having an alkanol with 1 to 8 carbon atoms. In this process, the alcohol byproduct is separated from 2-methyl-gamma-butyrolactone in the second step. This separation can be effected by simple distillation. Although azeotropic distillation is not required, a separation of the alcohol remains a necessary step in the process of producing 3-methyl-tetrahydrofuran.
Alpha-methylene-gamma-butyrolactone is a reactive monomer. Direct catalytic conversion of alpha-methylene-gamma-butyrolactone to 3-methyl-tetrahydrofuran has been attempted in the past. But owing to the high temperature required for the catalytic reaction (greater than 15020  C.), the conversion results in polymerization of the xcex1-methylene-xcex3-butyrolactone.
Thus, the problem to be solved is to provide a simple, economical, one-step process for the production of 3-methyl-tetrahydrofuran. The one step process of the present invention describes a more efficient route to produce 3-methyl-tetrahydrofuran from xcex1-methylene-xcex3-butyrolactone with novel catalyst systems, without any alcohol production, thereby eliminating the step of azeotropic or any other type of separation.
This invention relates to a chemical process for producing 3-methyl-tetrahydrofuran, which comprises the step of hydrogenating alpha-methylene-gamma-butyrolactone, represented by the compound of formula (I), to yield 3-methyl-tetrahydrofuran (II) as product, (in the presence of a catalytic metal). 
By xe2x80x9calpha-methylene-gamma-butyrolactonexe2x80x9d is meant the compound described by the formula below. 
By xe2x80x9cacid promoterxe2x80x9d is meant a compound that is acidic in nature which is added to enhance the physical or chemical function of a catalyst.
By xe2x80x9cmetal promoterxe2x80x9d is meant a metallic compound that is added to enhance the physical or chemical function of a catalyst.
The acid and metal promoters are chemical promoters generally used to augment the activity of catalyst agents. The promoter may be incorporated into the catalyst during any step in the chemical processing of the catalyst constituent.
This invention relates to the synthesis of 3-methyl-tetrahydrofuran from alpha-methylene-gamma-butyrolactone. More specifically, this invention relates to synthesis of 3-methyl tetrahydrofuran in a single chemical step process from alpha-methylene-gamma-butyrolactone. The chemical process does not generate alcohol as a side product. The final product does not need separation or purification of alcohol. Owing to the high temperature of the catalytic reactions (greater than 150xc2x0 C.), previous attempts to directly convert alpha-methylene-gamma-butyrolactone to 3-methyl-tetrahydrofuran have resulted in the formation of a polymer of alpha-methylene-gamma-butyrolactone monomer.
The present method involves hydrogenation of alpha-methylene-gamma-butyrolactone to yield 3-methyl-tetrahydrofuran as product. A metal catalyst, with or without a support, may be present to effect the hydrogenation reaction. An acid material may optionally be used as a promoter to aid the reaction. A metal may also be optionally used as a promoter to aid the reaction.
The process of the present invention may be carried out in batch, sequential batch (i.e., a series of batch reactors) or continuous mode in any of the equipment customarily employed for continuous process. The condensate water is optionally removed from the reaction mass with the aid of an inert gas purge.
The temperature of the process is controlled in order to achieve a high yield of 3-methyl-tetrahydrofuran. A temperature range of from about 100xc2x0 C. to about 250xc2x0 is employed for the reaction. A temperature range of from about 200xc2x0 C. to about 250xc2x0 C. is preferred. A more preferred temperature range is from about 220xc2x0 C. to about 230xc2x0 C.
A pressure range of from about 3.4 MPa to about 14.0 MPa is employed in the reaction. Pressure range of from about 5.1 MPa to about 10.4 MPa is preferred. A more preferred pressure range is from about 5.1 MPa to about 6.9 MPa.
As used herein, a catalyst is a substance that affects the rate of the reaction but not the reaction equilibrium, and emerges from the process, chemically unchanged. A chemical promoter generally augments the activity of a catalyst. The promoter may be incorporated into the catalyst during any step in the chemical processing of the catalyst constituent. The chemical promoter generally enhances physical or chemical function of the catalyst agent, but they can also be added to retard undesirable side reactions.
Hydrogenation of alpha-methylene-gamma-butyrolactone to 3-methyl-tetrahydrofuran is effected in presence of a catalytic metal. The principal component of the catalyst is selected from the group consisting of palladium, ruthenium, rhenium, rhodium, iridium, platinum, compounds thereof, and combinations thereof.
The catalytic metal used in the process disclosed here may be used as a supported or as an unsupported catalyst. A supported catalyst is one which in which the active catalyst agent is deposited on a support material by spraying, soaking or physical mixing, followed by drying, calcination, and if necessary, activation through methods such as reduction or oxidation. Materials frequently used as support are porous solids with high total surface areas (external and internal) which can provide high concentrations of active sites per unit weight of catalyst. The catalyst support may enhance the function of the catalyst agent. A catalyst which is not supported on a catalyst support material is an unsupported catalyst. The support material is selected from the group consisting of carbon, alumina, silica, silica-alumina, titania, and a combination thereof. Moreover, supported catalytic metals may have the same supporting material or different supporting material. A preferred support is carbon. The carbon can be a commercially available carbon such as Calsicat C, Sibunit C, or Calgon C (under the trade name Centaur(R)).
A preferred catalytic metal content range in a supported catalyst is from about 0.1% to about 15%. A more preferred catalytic metal content range is from about 1% to about 7%. A further preferred catalytic metal content range is from about 1% to about 5%.
Preferred combinations of catalytic metal and support system includes palladium on carbon combined with rhenium on carbon, and rhodium on carbon combined with rhenium on carbon.
An acid promoter may be used in the reaction of the present invention. Suitable promoters include those acids with a pKa less than about 4, preferably with a pKa less than about 2, including inorganic acids, organic sulfonic acids, heteropolyacids, perfluoroalkylsulfonic acids, and mixtures thereof. Also suitable are metal salts of acids with pKa less than about 4, including metal sulfonates, metal trifluoroacetates, metal triflates, and mixtures thereof including mixtures of salts with their conjugate acids. Specific examples of promoters include sulfuric acid, fluorosulfonic acid, phosphoric acid, p-toluenesulfonic acid, benzenesulfonic acid, phosphotungtstic acid, phosphomolybdic acid, trifluromethanesulfonic acid, 1,1,2,2-tetrafluroethanesulfonic acid, 1,2,3,2,3,3-hexapropanesulfonic acid, bismuth triflate, yttrium triflate, ytterbium triflate, neodymium triflate, lanthanum triflate, scandium triflate, and zirconium triflate. A preferred promoter is selected from Zn(BF4)2,CBV-3020E zeolite, and 20 A zeolite. The acid promoter is used in concentration of from 0.1% to 5% by weight. A preferred concentration range is 0.25% to 2.5%.
Suitable heterogeneous acid promoters are zeolites, fluorinated alumina, acid-treated silica, acid treated silica-alumina, acid treated clays, heterogeneous heteropolyacids and sulfated zirconia.
A metal promoter may be used optionally with the acid promoter in the method of the present invention. Suitable metal promoters include tin, zinc, copper, gold, silver, and combinations thereof. A preferred metal promoter is tin.
The following abbreviations are used in the Examples:
A commercially available support such as carbon, alumina, silica, silica-alumina, titania available from Engelhard Corp. (E. Windsor, Conn.) was impregnated by incipient wetness with a metal salt. The precursors used were NiCl2.6H2O (Alfa Chemical Co.), Re2O7 (Alfa Chemical Co.), PdCl2(Alfa Chemical Co.), RuCl3.xH2O (Aldrich Chemical Co.). H2PtCl6 (Johnson Matthey, W. Deptford, N.J.), CrCl3.6H2O (Mallinckrodt Baker, Inc.), 5% Rh using RhCl3.xH2O (Alfa Chemical Co.). The samples were dried and reduced at 300-450xc2x0 C. in H2 for 2 hours.
The carbon used was commercially available as Calsicat Carbon, Sibunit Carbon, or Calgon Carbon (Centaur(R)). Calsicat Carbon is lot no. S-96-140 from Engelhard Corp, Beachwood, Ohio Sibunit Carbon is Sibunit-2 from Institute of Technical Carbon, 5th Kordnaya, Omsk 64418, Russia. Calgon Carbon is PCB Carbon from Calgon Corp. (under the registered trademark of Centaur(R)).